[evunveot]

>Imagine a world with double the amount of people living in it.

I find it mildly disturbing that the author assumes everyone reading this sentence is going to agree that it's an ominous prospect. Obviously, the implication is that it would be a world of fourteen billion people the vast majority of whom are on the brink of starvation, but we've (as a species) overcome Malthusian obstacles before. Why shouldn't having as many thriving human lives as possible be a goal worth striving for? If every human life has intrinsic (not to mention economic and cultural) value, then declining reproductive rates are a form of opportunity cost, not "one of the most important ... achievements in human history." And if we can't agree (or at least agree to act as if) every human life has intrinsic value, we're on our way to undermining the foundations of peaceful coexistence.

[quotemstr]

FWIW, this idea is what philosophers call "the repugnant conclusion", and the problem it presents is largely unsolved in normative ethics. It's one reason that I don't think formal ethical reasoning is a useful activity: in the end, we do what feels right or wrong, and we can't reason ourselves into a feeling.

https://plato.stanford.edu/entries/repugnant-conclusion/